The present invention relates to novel compounds which are carbacyclin analogs, to processes for the preparation of said carbacyclin analogs and the use of said analogs as pharmacological agents or as intermediates for the preparation of compounds useful as pharmacological agents. This invention also relates to chemical intermediates for preparing the novel carbacyclin compounds described and claimed herein.
Prostacyclin is an endogenously produced compound in mammalian species, being structurally and biosynthetically related to the prostaglandins (PG's). In particular, prostacyclin exhibits the structure and carbon atom numbering of formula I when the C-5,6 positions are unsaturated. For convenience, prostacyclin is often referred to simply as "PGI.sub.2 ". Carbacyclin, 6a-carba-PGI.sub.2, exhibits the structure and carbon atom numbering indicated in formula II when the C-5,6 positions are unsaturated. Likewise, for convenience, carbacyclin is referred to simply as "CBA.sub.2 ".
A stable partially saturated derivative of PGI.sub.2 is PGI.sub.1 or 5,6-dihydro-PGI.sub.2 when the C-5,6 positions are saturated, depicted with carbon atom numbering in formula I when the C-5,6 positions are saturated. The corresponding 5,6-dihydro-CBA.sub.2 is CBA.sub.1, depicted in formula II when the C-5,6 positions are saturated.
As is apparent from inspection of formulas I and II, prostacyclin and carbacyclin may be trivially named as derivatives of PGF-type compounds, e.g., PGF.sub.2 .alpha. of formula III. Accordingly, prostacyclin is trivially named 9-deoxy-6,9.alpha.-epoxy-(5Z)-5,6-didehydro-PGF.sub.1 and carbacyclin is named 9-deoxy-6,9.alpha.-methano-(5Z)-5,6-didehydro-PGF.sub.1. For description of prostacyclin and its structural identification, see Johnson, et al, Prostaglandins 12:915 (1976).
In naming the novel compounds of the present invention in general the art-recognized system of nomenclature described by N. A. Nelson, J. Med. Chem. 17:911 (1974) for prostaglandins is followed. As a matter of convenience, however, the novel carbacyclin derivatives herein are named as 6a-carba-prostaglandin I.sub.2 compounds, or as CBA.sub.1 or CBA.sub.2 derivatives.
In the formulas herein, broken line attachments to a ring indicate substituents in the "alpha" (.alpha.) configuration, i.e., below the plane of said ring. Heavy solid line attachments to a ring indicate substituents in the "beta" (.beta.) configuration, i.e., above the plane of said ring. The use of wavy lines (.about.) herein will represent attachment of substituents in the alpha or beta configuration or attached in a mixture of alpha and beta configurations. Alternatively wavy lines will represent either an E or Z geometric isomeric configuration or the mixture thereof. Also, solid and dotted lines used together, as for example, in formulas I and II at C-5,6 positions indicates the presence of either a double bond or alternatively a single bond.
A side chain hydroxy at C-15 in the formulas herein is in the S or R configuration as determined by the Cahn-Ingold-Prelog sequence rules, J. Chem. Ed. 41:16 (1964). See also Nature 212:38 (1966) for discussion of the stereochemistry of the prostaglandins which discussion applies to the novel carbacyclin analogs herein. Molecules of carbacyclin have several centers of asymmetry and therefore can exist in optically inactive form or in either of two enantiomeric (optically active) forms, i.e., the dextrorotatory and laveorotatory forms. The racemic form of carbacyclin contains equal numbers of both enantiomeric molecules. For convenience, reference to carbacyclin or CBA.sub.2 or CBA.sub.1 will refer to the optically active form thereof.
A formula as drawn herein which depicts a prostacyclin-type product or an intermediate useful in the preparation thereof, represents that particular stereoisomer of the prostacyclin-type product which is of the same relative stereochemical configuration as prostacyclin obtained from mammalian tissues or the particular stereoisomer of the intermediate which is useful in preparing the above stereoisomer of the prostacyclin type product. As drawn, formula I corresponds to that of PGI.sub.2 endogenously produced in the mammalian species. In particular, refer to the stereochemical configuration at C-8 (.alpha.), C-9 (.alpha.), C-11 (.alpha.) and C-12 (.beta.) of endogenously produced prostacyclin. The mirror image of the above formula for prostacyclin represents the other enantiomer.
The term "prostacyclin analog" or "carbacyclin analog" represents that stereoisomer of a prostacyclin-type product which is of the same relative stereochemical configuration as prostacyclin obtained from mammalian tissues or a mixture comprising stereoisomer and the enantiomers thereof. In particular, where a formula is used to depict a prostacyclin type product herein, the term "prostacyclin analog" or "carbacyclin analog" refers to the compound of that formula or a mixture comprising that compound and the enantiomer thereof.